The disclosure relates to a brake disk having the features described below, of the kind used for disk brakes of motor vehicles, for example.
To reduce wear and thereby increase service life, there is a known practice of providing brake disks with a wear-reducing surface coating. Wear-reducing surface coatings are applied thermally by flame spraying or arc spraying, for example, and contain chromium carbides and/or tungsten carbides, for example. The brake disk can be provided with the surface coating all over, although surface coating on friction surfaces of the brake disk is sufficient. Friction surfaces are the brake disk surfaces in the form of perforated circular disks against which the friction brake linings are pressed during braking. Apart from reducing wear, a surface coating can serve to protect against corrosion and/or improve braking properties of a brake disk.
In the case of uncoated brake disks, a brake disk thickness can be measured in order to check whether a wear limit has been reached and to assess whether the brake disk must be replaced. In the case of surface-coated brake disks, that is not possible because the surface coating is too thin and a thickness measurement, using a vernier caliper for example, would therefore be too inaccurate. Moreover, a brake disk has a thickness tolerance in its production, and this may be greater than the thickness of the surface coating. As a result, a new brake disk of which the thickness is at a lower production tolerance limit may be thinner, including its surface coating, than a brake disk, the thickness of which is at an upper production tolerance limit and the surface coating of which is worn.
Uncoated brake disks having a wear indicator or a plurality of wear indicators are also known. Such wear indicators consist of depressions, e.g. slots or holes, in the friction surfaces of the brake disk. If the depressions begin to disappear due to wear on the brake disk, this is a sign that the brake disk is worn and must be replaced.